A reactor that went dark in 2019 is being brought back to life at Three Mile Island, the Pennsylvania site synonymous with the worst nuclear accident in United States history. The revival is not a utility decision about ordinary demand. It exists because a single technology company needs enormous, around-the-clock electricity to run artificial-intelligence data centers, and it has agreed to buy every watt the plant produces.
The arrangement pairs Microsoft, which will consume the output, with Constellation Energy, which owns the plant and is doing the physical restart. It has become a marquee example of how the AI boom is reshaping the power grid, reaching back to reopen a reactor that its owner once judged too unprofitable to run.
The deal that revived a shuttered reactor
Constellation announced in 2024 that it would restart the undamaged Unit 1 reactor at Three Mile Island in a $1.6 billion project, with Microsoft agreeing to purchase the plant’s entire 835-megawatt output to power its data centers. The plant near Harrisburg is slated to begin generating again in 2027, according to the Pennsylvania Capital-Star. The reactor being restarted is not the one that suffered a partial meltdown in 1979; that unit, permanently disabled in the accident, is a separate reactor and remains out of service. Unit 1 ran for years after the accident and operated until Constellation closed it in 2019 for purely economic reasons, a decision the company has since called a mistake.
The power-purchase agreement runs 20 years, far longer than the wind and solar contracts technology firms have typically signed, a reflection of both the scale of AI’s appetite and the value of electricity that flows every hour regardless of weather.
Ahead of schedule and staffing up
The plant, rebranded as the Crane Clean Energy Center after a former Constellation chief executive, has been moving faster than its original timeline. Constellation has said the project is ahead of schedule, having pulled its target forward after securing accelerated grid-interconnection approval, the company reported. Rehiring and retraining a workforce is a central part of the effort, since a restarted reactor needs licensed operators, engineers and maintenance crews long before it produces power. Reactor operators must complete extensive training and obtain federal licenses to run the plant, a process that takes many months.
Clearing the regulatory path
Restarting a reactor is not a matter of flipping a switch; it requires approvals from multiple federal agencies. Constellation cleared important hurdles in 2026, with the Nuclear Regulatory Commission and the Federal Energy Regulatory Commission granting fuel-license and waiver requests, and the plant advancing toward fuel delivery while approaching full staffing, as the American Nuclear Society reported in a mid-2026 update. The NRC has also issued for public comment a draft finding that the restart would carry no significant environmental impact, a step toward the final approvals the plant still needs. The federal government has backed the effort financially as well, with the Department of Energy closing a $1 billion loan intended to lower the project’s borrowing costs, according to federal project disclosures.
Why AI is reaching for nuclear power
The logic behind reopening a reactor is the peculiar shape of data-center demand. AI training and inference run continuously and draw steady, massive loads, the kind of profile that intermittent renewables cannot match on their own. Nuclear plants, by contrast, generate carbon-free electricity at high output every hour of every day, which is precisely what a hyperscale operator wants behind its servers. The 835 megawatts headed to Microsoft is roughly equivalent to the electricity used by hundreds of thousands of homes, redirected entirely to computing infrastructure. For a company positioning itself at the front of the AI race, locking up a dedicated, reliable, low-carbon supply is as strategic as buying the chips.
A grid straining under new demand
The Three Mile Island restart is one answer to a larger problem: electricity demand is climbing after decades of near-stasis, driven heavily by data centers, and new supply is struggling to keep pace. Regional grid operators have warned that data-center growth is outrunning the addition of new generation, raising concerns about both reliability and consumer costs. That tension has made projects like Crane politically attractive, framed as reviving a domestic asset and winning the AI race at once, even as consumer advocates warn that ratepayers should not shoulder the cost of infrastructure built to serve big technology firms. The restart also sits within a broader trend, with other mothballed reactors being brought back and technology companies pursuing their own nuclear deals. What was once unthinkable, restarting a reactor at the site of America’s most notorious nuclear accident, has become a signature move of the AI era, and its success or delay will be watched as a test of whether the grid can be scaled fast enough to match the computing it is being asked to feed.
A template other companies are watching
The significance of the Three Mile Island restart extends well beyond a single plant. It has become a proof of concept for a new kind of energy arrangement, in which a technology company underwrites the revival of a large, dispatchable power source by committing to buy its entire output for decades. That structure gives a plant operator the financial certainty needed to justify a costly restart, and it gives the buyer a dedicated supply insulated from the volatility of the open market. If the Crane project comes online as planned, it will validate a model that other operators and other tech firms are already exploring for additional shuttered reactors.
It also crystallizes a broader debate about who pays for the AI build-out. Supporters frame deals like this as private capital solving a public problem, adding carbon-free capacity that benefits the whole grid without burdening ordinary ratepayers. Critics counter that the surge of data-center demand is driving up prices for everyone, and that dedicating an entire reactor to one company’s servers does nothing to relieve the strain households feel. Both readings can be partly true at once, which is why the restart is being watched not only as an engineering milestone but as a test of how the costs and benefits of the AI era will be distributed. The reactor’s return, at a site whose name still evokes nuclear disaster, is a measure of how far the calculus has shifted.
This article was produced with AI assistance and reviewed by Morning Overview editors.
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